---临时浅拷贝-非嵌套表
local clear = reload("table.opt.clear")
local temp = {}
local meta = {}
local read = {}
function meta.__index(t, k)
    return temp[k] or read[k]
end

local once = {}
setmetatable(once, meta)

return function (r)
    read = r
    clear(temp)
    return once
end
